Mobile communication devices wirelessly connect to mobile communication networks via radio access networks, which are usually configured as radio cellular networks comprising a plurality of radio cells. Each radio cell covers certain geographical area and is served by a base station which forms the access point to the radio access network in the radio cell.
In modem mobile communication system, some geographical areas may be covered by multiple radio cells. Such area may be covered by a first radio cell, which is covered totally by a larger second radio cell of the same radio access technology. In this configuration, the second radio cell may provide continuous coverage of the area, while the first radio cell increases the capacity of a special subarea, such as a hotspots, homes or business mall or offices. Such radio cells are particularly known as so-called Micro Radio cells, Pico Radio cells and Femto Radio cells.
Similarly, a first radio cell of a first radio access network may be covered by a second radio cell implementing a different radio access technology than the first radio cell. In particular, the second radio cell may implement a legacy radio access technology and may be deployed to provide basic coverage of voice or lower-speed data services, while the first radio cell enhances the capability of the area to support high-speed data or multimedia services.
In view of the aforementioned configurations in which one geographical area is covered by two radio cells, the document TR 32.826 (version 10.0.0) of the 3rd Generation Partnership Project (3GPP) suggests to deactivate radio cells in order to save energy. In the aforementioned first scenario, the first radio cell may be deactivated in case that light traffic or no traffic is detected in the first radio cell, and in the second scenario, the first radio cell may be deactivated in case that no high-speed data or multi-media traffic is detected in the radio cell.
One further approach for energy saving suggested in TR 32.826 is to concentrate the load into a few selected radio cells that remain active during low traffic demand periods with increased coverage area and to deactivate the remaining less loaded radio cells. These radio cells may only be activated in peak time situations in which each radio cell may cover a smaller geographical area to cope with peak time traffic demand.
When a radio cell is deactivated, mobile communication devices which are located in the radio cell and are engaged in an active speech or data connection with the mobile communication system have to perform a handover procedure to change into a new radio cell covering the geographical area of the radio cell to be deactivated. In the handover procedure, the connection is switched over from the old radio cell to be deactivated to the new radio cell such that it can be continued therein.
Using standard procedures, mobile communication devices in idle mode, i.e. mobile communication devices that are switched on but do not have any established speech or data connection to the mobile communication network, will recognize the deactivation of a radio cell they are camped on due to measurements of the signal strength in their serving radio cell, which are performed essentially continuously. When those mobile communication devices determine that the radio cell no longer exists, they will select a new radio cell covering the relevant geographical area and will try to register in such radio cell by exchanging corresponding messages with the mobile communication network.
All mobile communication devices which were located in the deactivated radio cell will perform the registration procedure in a new radio cell essentially simultaneously. This will lead to peak signaling loads in the mobile communication network. As a consequence, the mobile communication system may become overloaded and additional efforts are needed to dimension the mobile communication network to cope with the peak signaling load.